1. Field of the Invention
This invention relates generally to saws for high stress cutting of hard materials including metals and plastics. More particularly, the invention pertains to hand saws for use with conventional hack saw blades.
2. State of the Art
Hack saws have been in use for many decades, and have taken several forms. They are typically designed for cutting metal or other hard materials, and because of the high resistance offered by such materials, require strong frames to withstand high axial forces tending to bend the frames.
In the construction trades, conventional hack saws are used to cut pipes, tubing, sheet metal, plastic foam sheeting, fiberboard, and even bricks and the like. Various blades are available for cutting specific materials. High arm forces are often required to overcome the resistance to cutting of such materials, and hack saws are often used overhead, or in narrow or otherwise confined spaces. The high forces used sometimes break the hack saw blade, or even the saw frame, as is well known to those in the construction trades.
An early hack saw design is shown in U.S. Pat. No. 1,190,477 of Sprague. Both ends of the blade are adjustable on the frame to vary the cutting depth, but the maximum cutting depth appears to be less than 4 inches (10.16 cm.), assuming the blade pictured is a conventional long hack saw blade of 10 inches length. Furthermore, the frame uprights are not adjustable in length and project toward the workpiece being cut, making the blade adjustability of limited value.
Various hack saw apparatus are shown in U.S. Pat. No. 2,102,782 of Blum, U.S. Pat. No. 2,213,841 of Hubeck, U.S. Pat. No. 2,221,231 of Cassidy, U.S. Pat. No. 2,799,309 of Olesen, U.S. Pat. No. 3,822,731 of Keymer, and U.S. Pat. No. 4,256,156 of Biszantz et al. Various blade attachment devices and handle configurations are described. The Olesen patent describes a knob-shaped handle attachable to a hack saw frame. The purpose of the handle is stated to be for exerting high forces on the saw with a free hand. As is readily seen, any hand movement which tends to turn the knob may loosen the handle and cause it to slide on the saw frame. Moreover, the knob is of such a width that it interferes with cutting within a relatively narrow space.
Several versions of coping saws are illustrated in U.S. Pat. No. 803,694 of Jones, U.S. Pat. No. 903,495 of Parsons, and U.S. Pat. No. 1,929,989 of Priest. Coping saws have weak blades of small cross-section and length, and are used for cutting soft materials such as wood and soft plastic. Such saws have also been called "scroll" saws inasmuch as the thin blade may be rotated while cutting to form complex arcuate cuts. Coping saw frames and blades cannot tolerate high forces typical in the use of hack saws. Unlike hack saw blades, coping saw blades have a thin pin at each end for attachment to the saw frame. The blade is attached so that the saw cuts on the pulling stroke, rather than the pushing stroke, to prevent damage to the blade or frame.
U.S. Pat. No. 948,151 of Ullrich shows a miniature saw for use by jewelers.
Hack saws with very limited cutting depth are shown in U.S. Pat. No. 244,666 of Kaywood as well as in U.S. Pat. No. 325,506 and U.S. Pat. No. 5,063,675, both of Michas et al. Because of the limited size of the saw frame, the saw is typically operated with only one hand, making precise cutting difficult.
European Patent Application No. 88850104.6 of Sandvik shows a handle to which one end of a hack saw blade is attached. A central portion of the blade floats in a slot in an arm. The saw may be used in confined spaces, but the blade will not withstand any substantial force without bending, since the blade is not in tension and depends only upon its own resistance to bending.
None of the above noted documents show a hack saw suited for high stress application which has a cutting depth of more than about 4.0 inches (10.16 cm.). Furthermore, the applicant, being a construction contractor in the building trades, is unaware of the commercial availability of a high-clearance hack saw.
None of the above patents shows a hack saw of low cutting depth which may be readily used for precision cutting in closely confined spaces.
Many of the hack saws shown in the documents have very complex construction leading to high production costs.
The need for an inexpensive hack saw construction resulting in improved utility under rigorous use is resolved by the invention described below.